Mechanical links, unlike adhesive bonds or welded connections, are links that can be disassembled.
One method that is often used to create mechanical links between composite structures or panels is to use multiple interfacing metal parts, each attached to the composite at discrete locations, and to use mechanical attachment means, such as screws, pins, bolts, or other means.
Although these solutions may appear to be optimized, that is not so, because they do not withstand stress uniformly over the entire wall of the composite structure.
This generates local over stress that resulting in a risk of progressive failure originating in the most stressed areas, a phenomenon called peeling.
In addition, these local over stresses are difficult to quantify through mechanical analysis, which degrades the reliability and optimization of the structure, thereby making the link difficult to guarantee.
It is conceivable to have multiple large structural composite parts, such as wind turbine blades, which can measure up to several dozen meters.
Wind turbine blades are made from composite materials that reduce movement in these parts, which decreases the attachment stress to be withstood.
These blades are usually made from multiple sections for easier transport and especially for transport by truck.
This therefore poses the problem of mechanically assembling the composite material parts in a solution that is mechanically optimized in terms of mass, particularly if the stress passed through the link is very high and complex, the link having to withstand mechanical stress, fatigue stress, and major environmental stress with a very high level of reliability.
Documents EP 1 584 817, EP 1 878 915, and WO 01/48378 disclose links between sections of wind turbine blades provided by multiple metal parts.
In document EP 1 878 915, the link uses metal rods inserts into the walls of the central casing and glued into place.
In document WO 01/48378, the links are distributed along the skin of the blade, and in document EP 1 584 817, separate ties, securely attached to the central casing, are attached together and consolidated by items that cover the gap between blades.
These embodiments use discrete mechanical attachment means.
Moreover, there are known methods for calculating metal/composite links using pins, although such calculations are quite complex because all phenomena to be taken into account, including the transfer of stress between the composite and the pins, shear in the pins, matting of the composite, the tensile strength of the composite and/or the metal, and scribing.
It should be noted that the known methods for calculating the transfer of stress are highly approximate, since they simplify the geometry of the assembly by representing them as a simple shear, making it possible to use the method for calculating shear, known as the Huth method.
Because of this approximation, traditional methods do not actually perform a thorough parametering of the links.
Specifically, the Huth method does not examine asymmetrical geometric links, which limits its scope of use.
Moreover, the calculations associated with this model, particularly for calculating the shear in the pins, cannot be extended for multishear, case in which such model is not at all adapted.
Document FR 2 675 563 discloses a method of linking a composite tube and a metal tube.
In this method, the metal part is attached to the composite both by an adhesive bond and by mechanical attachments, allowing possible mechanical flux to be higher. However, this method, for which optimizing the pin link depends on the orientation of the winding wires, is specific to coiled tubes and therefore specific to a particular method of manufacturing the composite material.
This concept does not apply directly to composite parts, such as sections of wind turbine blades, which are not usually manufactured by coiling and whose fibers are oriented as determined by the constraints of using those blades.